Bladder reconstruction plays an essential role in the treatment of voiding disorders characterized by low bladder capacity or high intravesical pressures or both-1 The ideal material should be biocompatible and mechanically reliable, resist extraluminal infection, deter or tolerate intraluminal infection, and be easy to implant surgically. The material should preserve renal function, provide adequate urinary storage at low pressure and allow volitional, complete evacuation of urine per urethram. To achieve this goal, autoaugmentation techniques and a great variety of synthetic and naturally derived biomaterials have been used.
Synthetic materials have been unsuccessful because of foreign-body reactions, resulting in stone formation, collapse, infection, rejection, or extrusion and migration of the graft (see Barrett, et al. Semin. Urol. 2:167-75 (1984); Bohne, et al. J. Urol. 77:725-732 (1957); Stanley, et al. J. Urol. 107:783-787 (1972); Swinney, et al. Br. J. Urol. 33:414-429 (1961)). As a result, synthetic materials have been used primarily as temporary implants to allow bladder regeneration to occur (see Taguchi, et al. J. Urol. 108:752-756 (1977); Tsuji, et al. J. Urol. 97:1021-1028 (1967)). However, the majority of studies confirm regeneration of transitional cell epithelial lining on the inner surface of the graft without adequate reconstruction of a functional detrusor muscle. Natural materials for bladder reconstruction have mostly retracted with time (see, Baret, et al. Surg. Gynec. Obstet. 97:633-639 (1953); Kelami, J. Urol. 105:518-22 (1971)) and the alloplastic total bladder prosthesis is still at an investigational stage in animals.
Autoaugmentation by enterocystoplasty with either small bowel or colon has well-documented urodynamic benefits. Sidi, et al. J. Urol. 136:1201-4 (1986). Because of complications, including metabolic acidosis (McDougal, J. Urol. 147:1199-208 (1992)) rupture (Bauer, et al. J. Urol. 148:699-703 (1992)), mucus production, chronic bacteriuria, stone formation (Golomb, et al. Urology 34:329-38 (1989)), and the potential for osteoporosis and malignancy (Filmer, et al. J. Urol. 143:671 (1990)), the search for other suitable materials continues. Gastrocystoplasty circumvents some of these problems, but peptic ulcers and perforations, the hematuria/dysuria syndrome, and metabolic alkalosis negate some of its potential advantages over intestinal segments. Mitchell, et al. Oxford, Blackwell Scientific, pp 439-444 (1993). Recently the technique for enterocystoplasty lined with urothelium has been shown to increase bladder capacity while taking advantage of the inert properties of an intact urothelial lining. Buson, et al. Urology 44:743-748 (1994); Gonzales, et al. Urology 45:124-129 (1995). Gastrointestinal segments in general have proven to enhance bladder capacity and compliance, thus protecting the upper tract and renal function. Unfortunately, they are unable to support normal micturition, which often necessitates clean intermittent catheterization or other supportive measures to ensure complete bladder evacuation.
To overcome this functional shortcoming, natural and/or biodegradable materials serving as a scaffold for the ingrowth of host bladder wall components have been tried with encouraging results. Atala, et al. J. Urol. 150:608-12 (1993); Knapp, et al. J. Endourol. 8:125-30 (1994); Novick, et al. J. Biomed. Mater. Res. 12:125-47 (1978); Scott, et al. Br. J. Urol. 62:26-31 (1988). The bladder wall tissue thus regenerated has shown the potential to provide functional augmentation in terms of an enlargement of the bladder without compromising its voiding abilities.
Despite the above efforts, there remains a need for new materials which are useful for grafting by serving as a scaffold for the development of new muscle tissue. The scaffolding material should be antigenic and capable of use in a variety of organs and individual hosts. Surprisingly, the present invention provides such materials and further provides methods for their preparation and use.
In one aspect, the present invention provides an acellular matrix graft which is isolated from muscle tissue, and consists essentially of acellular collagen and elastin. The muscle tissue which is the source of the graft is, for example, bladder tissue or other smooth muscle tissue such as heart tissue or ureter or urethra tissue.
In another aspect, the present invention provides methods of preparing acellular matrix grafts in which muscle or nerve tissue is isolated and freed from cells and cellular components by mechanical, chemical or enzymatic methods, or by combinations of mechanical, chemical and enzymatic methods to leave a scaffold or graft which is essentially collagen and elastin fibers. For example, a bladder acellular matrix graft can be prepared by:
(a) removing mucosa from an excised bladder cap to provide a bladder wall;
(b) treating the bladder wall with chemical and enzyme agents to release intracellular components from the bladder wall to provide an intermediate matrix; and
(c) solubilizing and removing cell membranes and intracellular lipids from the intermediate matrix to provide a bladder acellular matrix graft which consists essentially of acellular collagen and elastin.
In yet another aspect, the present invention provides methods of restoring muscle function in animals having damaged or diseased muscles. In these methods, the damaged or diseased tissue is removed and replaced with an organ-specific acellular matrix graft. The surrounding tissue then grows and infiltrates the scaffold or graft such that muscle tissue is regenerated and muscle function is restored.
In one preferred embodiment, the method is directed to restoring bladder function in an animal having a partially damaged bladder, the method comprising:
(a) removing the portion of the bladder which is damaged; and
(b) replacing the removed portion with a bladder acellular matrix graft to promote regeneration of bladder tissue and restore the bladder function.
In still another aspect, the present invention provides methods for promoting regrowth and healing of damaged or diseased muscle tissues, said method comprising replacing the damaged or diseased muscle tissue with an acellular matrix graft which consists essentially of acellular collagen and elastin, and is prepared from organ-specific tissue.